Process for separating alcohols from mixtures of alcohols, water and other compounds

Abstract

From a mixture containing methanol, ethanol, n-propanol, isobutanol water and other high-boiling and low-boiling compounds, the claimed process enables three separate streams to be obtained, one an anhydrous stream of methanol or methanol and ethanol (I), one containing most of the n-propanol present in the feed mixture (II), and one containing most of the isobutanol present in the feed mixture (III), by using three fractionating columns.

We claim: 
     
       1. A process for separating a feed mixture of from 1 to 70 wt % methanol, from 0.1 to 10 wt % ethanol, from 0.1 to 20 wt % n-propanol, from 2 to 80 wt % isobutanol, from 0.1 to 50 wt % water, and the remainder to 100 wt % of low-boiling organic compounds and high-boiling organic compounds; comprising (a) feeding to a first fractionating column via a side inlet said feed mixture so as to discharge (i) from the top of said first column, a gaseous stream consisting essentially of a portion of said low boiling organic compounds; (ii) from a side outlet located at a point above said side inlet, an anhydrous liquid stream consisting essentially of a portion of said methanol, ethanol or a mixture thereof; and (iii) from the bottom of said column, a liquid stream consisting essentially of substantially all of said n-propanol, isobutanol, water and height-boiling compounds and a portion of said methanol, ethanol or mixture thereof;   (b) feeding said liquid stream of (a) (III) into a second fractionating column through a first side inlet so as to discharge (i) from the top of said second column, a stream comprising a portion of said n-propanol and a portion of said methanol, ethanol, isopropanol and water; (ii) from a side outlet below said side inlet, a liquid stream which, after cooling, is separated into an aqueous and an organic phase, said organic phase being recycled to a second side inlet immediately below said side outlet; and (iii) from the bottom of said column, a liquid stream comprising a portion of said isobutanol and high-boiling compounds; and   (c) feeding said aqueous phase of (b) (ii) to a third fractionating column so as to discharge (i) from the top of said column, an organic stream consisting essentially of methanol, ethanol, n-propanol, isobutanol and high-boiling compounds, which is recycled by being added to said feed mixture before the latter is fed to said first fractionating column and (ii) from the bottom of said first fractionating column and (ii) from the bottom of said column, a stream consisting essentially of water;   wherein said fractionating columns are operated in the range of 30 to 500K Pascal absolute.   
     
     
       2. A process as claimed in claim 1, wherein the feed mixture contains: from 5 to 30 wt % of methanol,   from 0.1 to 5 wt % of ethanol,   from 1 to 15 wt % of non-propanol,   from 25 to 70 wt % of isobutanol,   from 1 to 30 wt % of water,   the remainder to 100 wt % of low-boiling organic compounds and high-boiling organic organic compounds.   
     
     
       3. A process as claimed in claim 1, wherein said fractionating columns are operated in the range of from 100 to 300K Pascal absolute. 
     
     
       4. A process as claimed in claim 1, wherein an antifoaming solution is fed into the first fractionating column and/or the second fractionating column. 
     
     
       5. A process as claimed in claim 1, wherein an antifoaming solution is fed at a point immediately below the side outlet of the stream obtained in (a) (ii). 
     
     
       6. A process as claimed in claim 1, wherein an antifoaming solution is fed into said liquid phase obtained n (b) (ii). 
     
     
       7. A process as claimed in claim 1, wherein a solution of NaOH and/or basic compounds selected from the group consisting of carbonates, bicarbonates and phosphates of alkaline and alkaline earth metals, and/or basic nitrogenated compounds selected from the group consisting of amines and alkanolamines is added to the stream obtained in (a) (iii) or to the stream obtained in (b) (ii). 
     
     
       8. A process as claimed in claim 1, wherein the stream obtained in (b) (iii) is used to obtain isobutene by dehydration in the presence of a catalyst. 
     
     
       9. A process as claimed in claim 8, wherein the stream obtained in (a) (ii) is added to the isobutene obtained by dehydrating the isobutanol, to produce MTBE or MTBE and ETBE mixtures. 
     
     
       10. A process as claimed in claim 8, wherein part of the stream obtained in (a) (ii) is recycled to a reactor for synthesizing alcohols from CO and H 2 . 
     
     
       11. A process as claimed in claim 1, wherein the stream obtained in (b) (i) is recycled to the reactor for synthesizing alcohols from CO and H 2 . 
     
     
       12. The method of claim 1, wherein said liquid stream obtained in (a) (iii) is cold phase separated prior to (b) into an aqueous phase and an organic phase, and thereafter said organic stream is fed into said second fractionating column in (b) and said aqueous phase is combined with said aqueous phase obtained in (b) (ii) and fed into the third fractionating column in (c).